In recent years, it is demanded that base stations have a function of accommodating radio signals in various frequency bands and radio signals having different speed requirements, and performing signal processing on these radio signals at a high speed. Further, in recent years, there is an increasing importance of a radio-optical combination access network efficiently transporting various kinds of radio signals from respective base stations to accommodation stations connected to such as, for example, a metro network. An accommodation station has a built-in optical transport apparatus as an optical line terminating apparatus which optically transports, for example, an optical multiplexed signal accommodating radio signals per optical wavelength.
The optical transport apparatus assigns an optical wavelength to each port in a fixed manner using a fixed wavelength filter (AWG: Arrayed Waveguide Grating) having a plurality of ports, and transmits an optical wavelength assigned to a corresponding port from an optical multiplexed signal passing the ports. As a result, the optical transport apparatus can obtain an arbitrary optical wavelength from the optical multiplexed signal using the AWG, and obtain radio signals in the obtained optical wavelength.
When, in the optical transport apparatus, there occurs a free band in an optical wavelength accommodating radio signals, the utilization ratios of radio resources and optical wavelength resources decrease, resulting in deterioration of the transport efficiency of optical wavelengths. Because the optical transport apparatus uses the AWG, an optical wavelength assigned to each port is fixed, that is, a transmission bandwidth is fixed for each port. As a result, in the optical transport apparatus, it is difficult for the transmission bandwidths assigned to the ports to be changed, and an optical multiplexed signal is transported while the free band occurs in the optical wavelength, resulting in deterioration of the transport efficiency of the optical wavelengths.